1. Field of the Invention
This invention relates to refrigeration apparatus and more particularly to a receiver specially adapted to minimize the refrigerant needed in a refrigeration system.
2. Description of the Related Art
Refrigeration systems typically have a receiver downstream from the condenser as a separate component. A receiver provides storage of a volume of refrigerant sufficient to accommodate for variations in system operating conditions and loss of refrigerant. When the refrigeration system is not in operation, most of the refrigerant is contained in the receiver. Ideally, the system will have only the amount of refrigerant in it needed to accommodate its various operating conditions. This ideal amount can be calculated, and installers of the refrigeration system may be advised to charge the system with only that quantity of refrigerant plus the amount needed to ensure that only liquid refrigerant flows out of the receiver. However, a typical receiver has capacity for storing considerably more refrigerant than what is needed and the procedure followed by installers in charging a system results in more refrigerant being used than would seem to be necessary.
Many systems employ a device called a sight glass downstream from the receiver which provides a view to the refrigerant flowing from the receiver. When charging a system there is initially a mixture of liquid and vapor refrigerant flowing out of the receiver. Installers observe the mixture through the sight glass and are instructed to continue adding refrigerant until bubbles, which are indicative of vapor in the system, are no longer visible in the sight glass, because liquid covers the inlet to an outlet tube in the receiver. After bubbles are no longer observed, some installers will add more just to be certain that there is enough. This results in undesirable over-charging of the receiver. The present inventor has determined during the development of this invention that overcharging, which occurs in prior art systems, ranges from 25 to 35 percent of the volume of the receiver--more than double what was previously thought. Over-charging, of course, in effect, wastes refrigerant and adds to the cost of the system. With inexpensive refrigerants, this may not have been a very significant factor; however, because of environmental concerns, it is now required that different refrigerants are employed, and they are more expensive.
Construction of the receiver is one known factor which affects the quantity of refrigerant required to stop vapor bubbles from being observed in the sight glass. Basically the receiver comprises a container in which liquid refrigerant collects, with vapor refrigerant above the liquid. An outlet tube for withdrawing liquid from the receiver typically extends through an upper wall of the receiver and has an open lower end positioned near the bottom of the container. In order to withdraw only liquid from the receiver (a circumstance in which the receiver is said to have a liquid seal), it is necessary that the open lower end always be covered by liquid. But, as mentioned above installers filling systems which have a sight glass report that significantly more refrigerant is needed to create a liquid seal than simply that required to cover the mouth of the tube inlet. That additional quantity of refrigerant is essentially an unproductive percentage of the refrigerant from the cooling standpoint.
In some industrial applications, unproductive use of refrigerant has been reduced by adding a secondary reservoir at the bottom of the receiver into which the outlet tube extends. In this way, deeper insertion of the receiver outlet tube is possible so that less refrigerant is needed to provide the liquid seal.
Other commercial applications reduce refrigerant levels by tilting the receiver container so that the end of the container into which the outlet tube extends is the lower end, thus causing the refrigerant level at that end to increase. This means that for the same or less refrigerant, vapor-free flow down-stream from the receiver can be assured.
While both of these prior art approaches result in less refrigerant, they have their draw-backs. A secondary reservoir is inconvenient because it requires a special housing for ground clearance of the secondary reservoir. The method of tilting the receiver container is useful but fails to reduce the level of refrigerant needed for liquid seal close enough to the level needed for proper operation of the system. Thus, a need exists for an improved receiver design that will further minimize the refrigerant required.